Method of and apparatus for securing propeller blades in the hub



Jun 9, 1936- R. KRISSIEP El AL 2,043,431

METHOD OF AND APPARATUS FOR SECURING PROPELLER BLADES IN THE HUB Filed Sept. 20, 1954 In venfora:

AM W,

Patented June 9, 1936 UNITED STATES PATENT oFncr.

METHOD OF AND APPARATUS FOR SECUD- ING PROPELLER BLADES IN THE HUB Reinhard Krissiep, Frankfort-on-the-Main, and

Werner Linicus, Dusseldorf,

Germany, as-

signors to American Lurgi Corporation, New York, N. Y., a corporation of New York Application September 20, 1934, Serial No. 744,852 In Germany September 23, 1933 17 Claims. (Cl. 29-90) magnesium, it has been found that after a comparatively short time, the surfaces provided on the root or shank of the propeller blades, for mounting or securing them in the hub, exhibit cracks and other indications of damage, which lead to fractures and display decided evidence of frictional oxidation.

According to the present invention, these defects are remedied by employing propeller blades, the surface of which, provided on the root or shank of the latter, foi' securing or mounting them in the hub, is subjected to plastic deformation of the outer layer, and thereby compressed, by rolling or pressing. The essential feature therefore is that finished propellers are subjected to a supplementary surface treatment of shank or root, at ordinary temperature. In this coldworking process the external shape is fully maintained to within about 0.01 mm. Trials made with propeller blades treated in this manner have revealed a substantial improvement in durability, and thereby increased length of service, by comparison with untreated propellers. Moreover, corrosion phenomena are no longer detectable in propellers with fitting surfaces that have been treated in accordance with the present invention. Since the rolling or pressing treatment of the propeller roots or shanks according to the invention results in high dimensional accuracy and superficial smoothness, a firm seating in the hub ensues as a further advantage of the invention.

Moreover, according to the present invention, the pressure on the surface of the work is elastically distributed over two or more portions of its surface, in order to consolidate the surface of the shank or root of the propeller by the application of pressure in the cold, whilst maintaining a relative movement between the work and the tool. The result thereby attained is that the pressure exerted on the surface to be consolidated remains uniform, or approximately so at all points on which the pressure acts, not only in the case of round and centrically rotating bodies, but also in that of bodies of non-circular form or such as rotate eccentrically. This action is precisely of special importance in superficially consolidating the shanks or roots of finished propellers of light metal-and particularly of the alloy known under the registered trade mark Electron"the centric chucking of which in the pressing apparatus is not always practicable.

We have discovered that by subjecting the shank of an aeronautical propeller blade of light metal to a certain amount of cold work to form thereon 5 a uniformly smooth, dense and hardened outer skin, and by controlling the working operation so as to uniformly distribute and equalize the strains in the entire cold worked area to practically eliminate localized overstrains, we are able to increase 10 considerably the endurance limit of the propeller and render it substantially safe for aeronautical use.

'It is known that aeronautical metal propellers, and especially light metal propellers were un- 15 reliable and failed suddenly, particularly when operating at certain critical speeds which set up resonant vibrations and cyclic stresses of high intensity. These resonant vibrations were known to be particularly dangerous in causing gelling 2g started b the localization of cyclic overstresses 25 of high intensity at surface imperfections on the surface 0" the propeller shank, such as scratches, tool marks, etc. and that the initiation of and the rapid progression of fatigue cracks were accentuated y localized corrosion caused by non- 30 uniformity of the surface finish, by frictional oxidation, by localized overstrains, and by the difference in potential betweenthe magnesium alloy or other light metal or alloy of the propeller and the steel hub in which it was mounted. In con- 35 trast to prior propellers, actual tests have shown that metal propellers and especially magnesium alloy propellers which have been treated according to principles of the present invention have a safe fatique endurance limit, about or more 40 higher than that of untreated propellers, are not subject to galling or cracking of the shank, and in flight are able to withstand successfully the most severe service conditions.

Our process is particularly useful in treating 45 light magnesium alloy or other light metal propellers of the variable pitch type, in which the shank of each propeller blade is mounted in a steel hub and is subjected to vibrations and severe cyclic stresses of high frequency at the fas- 50 tening point. The shank is also known to be subject to the formation of hard spots and of frictional and oxidation corrosion at localized areas of the surface of the shank in contact with the 55 steel hub mounting.

According to the principles of the present invention, we impart to the shank of the propeller a uniformly dense and hard outer skin having a smooth surface by subjecting it to an appropriate and specially controlled cold working operation, such as by cold rolling, cold pressing, burnishing, etc. The amount of cold work applied to the shank is controlled so as to deform uniformly the surface layers only and produce a dense and hardened outer surface having a uniform finish substantially free from imperfections, such as scratches, tool marks, etc. Furthermore, we control the cold working operation so as to equally distribute and equalize the strains over the entire treated surface of the shank, thereby producing an outer surface which in addition to having a uniform finish is also uniformly hard and free from localized stresses. Another special feature of the invention is that by the cold working operation indicated hereinabove, the shank of the propeller can be finished to a higher degree of dimensional accuracy than it is possible with the usual machining operations. Thus, we have been able to finish the propeller shanks to within 0.01 mm. of the required size and obtain such accurate and close fit of the shank in the steel hub, that free play or loose motion of the propeller in the hub is reduced to a minimum. Moreover, it is to be observed that the hardness of the surface renders the shank more resistant to galling, while its uniform finish substantially devoid of localized overstrains, scratches etc., renders it more resistant to corrosion and erosion fatigue.

In carrying the present invention into practice, we cold work the shank of a magnesium alloy propeller by means of appropriate tools, such as rolls, rods, burnishing tools, etc. These compression tools are made to exert the desired pressure on the surface of the propeller shank and are controlled by suitable balancing or compensating devices so as to maintain a constant pressure at all areas of the surface treated irrespective of any eccentricity of the shank or of any irregularity of its shape. In-practice, we prefer to apply the required and suitably balanced pressure radially to at least three zones equally spaced around the surface of the propeller shank.

In order more clearly to understand the invention, reference is made to the accompanying drawing, which illustrates diagrammatically and by way of example, one embodiment of pressing apparatus and in which:-

The metal propeller, for instance a magnesium alloy propeller, root l, which is turning in the direction of the arrow, is surrounded by three radially disposed press tools, consisting of the rolls 2 seated on pistons 4 adapted to be displaced in cylinder 3. These cylinders are connected to a common conduit 5 containing a liquid or gaseous pressure medium supplied from the pressure tank 6 designed, at I, as a wind chest or compensating vessel.

If the round work-piece l revolves eccentrically, so that one of the pressure pistons l is obliged to give way, this deflection increases the pressure in the pipe 5, and thereby on the other pistons 4, with the result that these other pistons are able to follow the deflecting workpiece and balance the pressure. If the round work-piece I revolves centrically, but exhibits a slight superficial irregularity, for example at the point 8, this latter always forces one of the pistons 4 into its cylinder, every time, and thus also increases the pressure in the pipe 5. However, since, in such case, owing to the centric rotation of the round work-piece, the other pistons I cannot follow the latter-and thereby balance the increased pressure set up at one point-the balancing of the pressure is effected 5 by the fluid reservoir 1. In any case-as can be seen from the drawing-the pressure on the surface of the work is elastically distributed over two or more portions of its surface, in such a manner that the pressure applied to the surface 10 to be consolidated remains uniform, or approximately so, on said portions even when the work is non-circular or rotates eccentrically.

It will be directly evident from the foregoing description that the surfaces of work-pieces of 15 oval, fluted or other contour can be treated in the pressing apparatus according to the present invention, since the elastic distribution of pressure over two or more portions of the surface always ensures approximately constant pressure 20 being exerted at all the points at which the pressure is applied by the tools serving to consolidate the surface.

We claim:-

1. The method of consolidating the shank of a 25 metal aeronautical propeller and equalizing strains throughout the surface of said shank which comprises subjecting practically the entire surface of the shank to uniform rolling pressure to impart thereto a substantially dense outer skin, adjusting said pressure to cause said skin to be uniformly compressed substantially throughout the treated area, and continuing said rolling pressure to impart to said treated skin a substantially smooth finish which is substantially 35 devoid of localized over-strains.

2. The method of consolidating the shank of a magnesium alloy aeronautical propeller and equalizing strains throughout the surface of said shank which comprises axially rotating a mag- 40 nesium alloy propeller blade, applying pressure to the surface of the shank of the blade, and controlling said pressure to a substantially constant value at substantially all regions of said surface to impart thereto a substantially uni- 45 formly densifled outer skin freed from localized over-strains.

3. The method of consolidating the shank of a magnesium alloy aeronautical propeller and equalizing strains throughout the surface of said 50 shank which comprises axially rotating a magnesium alloy propeller blade, applying pressure to the surface of the shank thereof, maintaining said pressure to a substantially constant value at practically all regions of said surface to impart 55 thereto a substantially uniformly compressed outer skin, and continuing the application of said pressure to impart to said skin a substantially smooth finish substantially free from surface imperfections and substantially free from localized over strains.

4. The method of consolidating the shank of a magnesium alloy aeronautical propeller and equalizing strains throughout the surface of said shank which comprises axially rotating a magnesium alloy propeller blade, radially applying pressure to at least three regions of the surface of the shank thereof, compensating variations in said pressure due to eccentricity and the like to maintain a constant value thereof substantially at all regions of the treated surface to impart thereto a substantially uniformly densifled outer skin, and continuing the application of said compensated pressure to impart to said skin a substantially smooth finish substantially free from surface imperfections and substantially free from localized over strains. I

5. The method of consolidating the shank of a magnesium alloy aeronautical propeller and equalizing strains throughout the surface of said shank which comprises axiallyv rotating a magnesium alloy propeller blade, radially applying rolling pressure to at least three regions equally spaced on the surface of said shank, compensating variations in said pressure due to eccentricity and the like to maintain a constant value thereof substantially at all regions of the treated surface to impart thereto a substantially uniformly densified outer skin, and continuing the application of v 5 said compensated pressure to impart to said skin a substantially smooth finish substantially free from surface imperfections and substantially free from localized over strains.

6. The method of consolidating the shank of a 2'} magnesium alloy aeronautical propeller and equalizing strains throughout the surface of said shank which comprises axially rotating a magnesium alloy propeller blade, radially applying rolling pressure to three regions spaced at about g 12% from each other on the surface of said shank,

compensating variations in said pressure due to eccentricity and the like to maintain a constant value thereof substantially at all regions of the treated surface to impart thereto a substantially 3o uniformly densified outer skin, and continuing the application of said compensated pressure to impart to said skin a substantially smooth finish substantially free from surface imperfections and substantially free from localized over strains.

'2. An apparatus for consolidating the shank of w a metal aeronautical propeller and distributing strains throughout the surface of said shank which comprises means for axially rotating said propeller blade, means for applying pressure of a smooth pressure tool surface to said surface of the shank, and means for controlling said pressure to maintain said pressure to a substantially constant value at all regions of the surface of said shank.

8. An apparatus for consolidating the shank of a metal aeronautical propeller and distributing strains throughout the surface of said shank which comprises means for axially rotating a light metal propeller blade, means for applying pressure of a smooth pressure tool surface to at least three regions of said surface, and means for compensating said pressure to maintain said pressure to a substantially constant value at all regions of the surface of said shank.

9. An apparatus for consolidating the shank of a metal aeronautical propeller and distributing strains throughout the surface of said shank -,which comprises means for axially rotating a light metal propeller blade, three rollers equally spaced around the circumference of the shank of said propeller blade, means for radially forcing said rollers against the surface of said shank, and

means for equalizing the pressure of said rollers shank whereby the pressure of the rollers against the surface of the shank is compensated and is maintained to substantially constant value at all regions of the surface of said shank during the rotation thereof.

11. An apparatus for consolidating the shank of a metal aeronautical propeller and distributing strains throughout the surface of said shank which comprises means for axially rotating said propeller blade, three rollers equally spaced around the circumference of said shank, a hydraulic piston for each of said rollers for forcing the same against the surface of said shank, a common fluid conduit connecting said pistons, a common pressure fluid in said conduit for simultaneously actuating said pistons, and means for compensating differences in pressure of said fluid whereby the pressure of said rollers against the surface of the shank is compensated and is maintained to a substantially constant value at prac tically all regions of the surface of said shank during the rotation thereof regardless of any ec= centricity.

12. The method of consolidating the working area of surface of the shank of a metal aeronautical propeller and of equalizing strains in said consolidated area which comprises applying at a uniform pressure a smooth tool surface to the surface of the shank to be consolidated, and causing relative displacement of said shank and tool surfaces whereby a relatively thin, uniformly dense and hard outer skin will be imparted to said surface of the shank without substantially changing and deforming the metallic structure underneath said skin.

13. The method of consolidating the shank of a metal aeronautical propeller and of equalizing strains throughout the surface of said shank which comprises applying at a pressure a smooth tool surface to the surface of the shank to be consolidated, and causing relative displacement of said shank and tool surfaces to subject practically the entire surface of said shank to uniform work whereby a relatively thin, substantially dense and hard outer skin practically devoid of localized over-strains is obtained substantially without changing and deforming the metallic structure underneath said skin.

14. The method of consolidating the shank of a metal aeronautical propeller and of equalizing strains throughout the surface of said shank which comprises applying at a pressure a smooth surface to the surface of the shank to be consolidated, causing relative displacement of said shank and tool surfaces to subject practically the entire surface of said shank to uniform pressure to impart thereto a relatively thin and substantially dense outer skin, and adjusting said pressure to cause said skin to be uniformly densified substantially throughout the treated area and to be freed from localized over-strain substantially without changing and deforming the metallic structure underneath said skin.

15. The method of consolidating the working area of surface of the shank of a metal aeronautical propeller and of equalizing strains in said consolidated area which comprises producing a finished propeller, and subsequently subjecting a working area on the surface of the shank of the said finished propeller to uniform work to impart thereto a substantially uniformly dense and hard outer skin.

16. The method of consolidating the shank of a metal aeronautical propeller and equalizing propeller. subjecting practically the entire surface oftheshankofthesaidfinishedlishtmetalpropeller to uniform pressure at ordinary temperatures to impart thereto a substantially dense outer skin. and adjusting said pressure to cause said skin to be uniformly densifled substantially throughout the treated area and to be substantially freed from localised over-strains whereby high dimensional accuracy within about 0.01 mm.

and great superficial smoothness are obtained. 10

REHNHARD WERNER- LINICUS. 

